1. Field of the Invention
The present invention relates to a process for purifying a halogenated alkenylphenol polymer, more particularly, the invention relates to a process of producing a halogenated alkenylphenol polymer containing no impurities such as low molecular weight (i.e., less than about 400) halides, etc.
2. Description of the Prior Art
Compounds containing a halogen atom such as chlorine and bromine are important as flame retardants and various of such compounds are commercially available. However, halogen containing polymeric compounds known at present are few. Further, the properties of such halogen containing polymeric compounds can hardly be anticipated from those of conventional low molecular weight compounds. Accordingly, it can be expected that with the development of these halogen containing polymers new utilities other than flame retardants, and new fields, will be developed.
It is known that a polymer or copolymer of vinylphenol is an excellent reactive polymer, and processes for producing various derivatives thereof have been reported.
The inventors investigated preparing halogenated alkenylphenol polymers and the flame retardant effect of halogenated alkenylphenol polymers. In the production of such polymers, the separation and purification of the halogenated polymers which are the reaction products of the reaction are particularly important, and it is necessary to treat the polymers in a different manner than in the case of producing low molecular weight halogen compounds. That is, in this case it is necessary to completely remove reaction medium, unreacted halogen, hydrogen halide, etc., from the reaction product, and the removal of these impurities is insufficient by a mere simple washing and drying. The inventors confirmed that when these low molecular compounds remain in the polymer they accelerate the gelation of the polymer, and, in particular, they cause discoloring and the generation of an irritative odor at high temperature, which greatly reduces the usefulness of the polymer.
For example, when a halogenated alkenylphenol polymer is blended with an epoxy resin, a hardened resin is formed, but if the aforesaid low molecular weight materials remain in the halogenated alkenylphenol polymer, the hardening reaction is abnormally accelerated, which makes it impossible to obtain a blend having uniform quality. Furthermore, it is known that a blend of a halogenated alkenylphenol polymer and an epoxy resin has excellent heat resistance, but when these low molecular weight materials remain in the blend, the heat resistance of the blend is greatly reduced by the generation of gases and at the same time the blend discolors.
The inventors further found that in a halogenated alkenylphenol polymer unstable halogen bonded to the polymer exists in an amount of 0.1-3% by weight of the total amount of the polymer. The unstable halogen bond is assumed to be a substitution bond at the tertiary carbon atom of the polymer chain. This was indirectly confirmed by experiments involving treating o-bromophenol or p-xylylene dichloride, which is the low molecular weight model compound of the halogen compound. Also, it was confirmed that an .alpha.-halogen substituted product was partially formed in the halide of p-ethylphenol, which is the low molecular weight model compound of poly-p-vinylphenol. Therefore, it is clear that there is a partial halogen substitution in the polymer main chain of a vinylphenol polymer.
Since the tertiary carbon substituted halogen bond has a bond dissociation energy lower than an aromatic substituted halogen bond by about 20 Kcal/mole, the tertiary carbon substituted halogen bond is liable to be decomposed and a polymer containing such a tertiary carbon substituted halogen shows somewhat lower heat resistance. Thus, if such a polymer is used as a heat resistance resin, it is subject to defects such as discoloring, a reduction in bending strength, etc., upon heating.